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DURHAM, N.H. -- A University of New Hampshire
space scientist examining the atmosphere of the
Moon says new findings might prove useful in future
colonization of the lunar surface.

Antoinette Galvin, UNH research associate
professor in the Institute for the Study of Earth,
Oceans and Space, is co-author of a research paper
detailing new measurements of small amounts of
oxygen, silicon and aluminum in the moon's
atmosphere. The findings are based on observations
by the Suprathermal Ion Composition Spectrometer
(STICS) aboard the WIND spacecraft and appear
in the American Geophysical Union's publication
"Geophysical Research Letters."

Galvin, who recently joined the UNH faculty from
the University of Maryland, is the lead
co-investigator of the STICS sensor.

She explains that the moon does not have an
atmosphere like Earth. "If you look in almost any
textbook listing planetary atmospheres, the moon
will be listed as having 'none' or 'essentially none,'"
she points out.

The low lunar gravity (one-sixth that of Earth)
means that the moon has a smaller "escape velocity"
-- 1.5 miles per second compared to the Earth's 7
miles per second -- "so almost any atmosphere the
moon gets, it immediately drifts off or escapes into
space. That means the atmosphere must be
continuously replenished."

The lunar atmosphere is also only
1/100,000,000,000,000 that of Earth, and in fact is
often called the exosphere. For planets, the
exosphere is the tenuous part of the atmosphere
beyond the ionosphere that blends into space, says
Galvin. "The Earth's exosphere starts at 480
kilometers up. For the moon, you have the surface of
the moon and -- bang! -- the exosphere right next to
it."

The lunar atmosphere was first found by the Apollo
17 crew, which detected helium and argon.
Ground-based observations later found sodium and
potassium, but the question remained: since these
elements made up less than 10 percent of the moon's
atmospheric density, what other elements were
there?

In answer to that question, STICS detected what
are called "lunar pick-up ions." Galvin explains that
when atoms are struck by ultraviolet radiation from
the Sun, they absorb the energy and kick out an
electron, becoming ions. "Ions are subject to the
solar wind electric and magnetic fields -- we call it
being 'picked up' by the solar wind," says Galvin. The
pick-up ions can receive quite a boost in speed this
way and accelerate up to twice the
400-kilometer-per-second solar wind speed.

It was through its detection of pick-up ions that
STICS identified the oxygen, silicon and aluminum.

"But where does this atmosphere come from?" asks
Galvin. "The composition gives us a clue."

The helium probably comes from the solar wind
hitting the moon, she explains. "In this way, some of
the solar wind becomes part of the lunar
atmosphere. But the other elements observed, both
on the ground and by STICS, are either from
objects impacting the moon and vaporizing, or from
the moon itself." Some may be due to out-gassing
from the lunar interior. As for the aluminum and
silicon seen by STICS, the origin is most like
sputtering: the solar wind hits the lunar surface, and
knocks out atoms from that surface.

The STICS paper does not speculate as to the
original source of the lunar oxygen. It may come
from the disassociated molecules that contain
oxygen, such as water, or like the aluminum and
silicon may come from sputtering off the surface.
Galvin points out that NASA's Lunar Prospector
recently confirmed the presence of ice on the moon,
and some theorize that the ice seen at the lunar
poles may be accumulated from this thin atmosphere.

Scientists now believe that water molecules --
whether out-gassed or left from comet impacts --
migrate to colder regions, where they condense as
ice back into the ground. They suggest this is the
most likely way that ice may have collected in the
polar shadows.

"So if the moon was really airless, there would be no
collected H2O as ice," says Galvin. "This ice may be
used by future colonists."

She adds, "The surface itself may be a colony's
source for metals, such as the aluminum seen by
STICS, so these aspects also could be important for
colonization of the moon."

Lunar exploration also can help us learn more about
other heavenly bodies, says Galvin.

"The moon is not the only 'airless' body that in fact
has a thin atmosphere. Some planets, asteroids and
other moons have similar atmospheres. Any flyby or
orbit of these objects by other spacecraft should
look for pick-up ions. Then one will get an idea of the
origin of the atmosphere and even some information
on the composition of the surface."